A magnet freely suspended in a vibration magnetometer makes 10 oscillations per minute at a place A and 20 oscillations per minute at a place B. If the horizontal component of earth's magnetic field at A is `36xx10^(-6)T`, then its value at B is

Options

A. `36 xx 10^(-6)T`
B. `72 xx 10^(-6)T`
C. `144 xx 10^(-6)T`
D. `288 xx 10^(-6)T`

Answer

C

Explanation

`(T_(A))/(T_(B)) = sqrt(((B_(H))_(B))/((B_(H))_(A))) rArr (f_(A))/(f_(B))= sqrt(((B_(H))_(A))/((B_(H))_(B)))`
`rArr (((10)/(60))/((20)/(60)))^(2)= (36 xx 10^(-6))/((B_(H))_(B)) rArr (B_(H))_(B)= 144 xx 10^(-6)T`